Inositol-excreting yeast

ABSTRACT

A yeast cell, preferably Saccharomyces cerevisiae, which contains a functional stable recombinant DNA sequence that does not allow for the encoding of a negative regulator of phospholipid biosynthesis therein. In a preferred embodiment, the recombinant DNA sequence is an opil gene deletion which results in the deregulation of inositol or inositol-containing metabolites such as inositol-1-phosphate synthase. Moreover, there is a method for obtaining inositol, inositol-containing metabolites or phospholipids such as myo-inositol or inositol-1-phosphate. The method comprises the steps of genetically engineering a stable yeast cell, preferably Saccharomyces cerevisiae, to continually produce inositol, inositol-containing metabolites or phospholipids. Additionally, there is the step of then generating the inositol, inositol-containing metabolites or phospholipids. In a preferred embodiment, the genetically engineering step includes the step of altering the negative regulatory step involved in phospholipid biosynthesis to overproduce inositol, inositol-containing metabolites or phospholipids such as myo-inositol.

This is a continuation of application Ser. No. 08/165,182 filed on Dec. 2, 1993, now abandoned, which is a continuation of Ser. No. 07/640,495 filed on Jan. 14, 1991, now abandoned.

FIELD OF THE INVENTION

The present invention is related to the negative regulation of phospholipid biosynthesis in a yeast strain to produce excess inositol. More specifically, the present invention is related to the production of excess inositol from a diploid yeast strain, baker's yeast (Saccharomyces cerevisiae), for human or animal consumption.

BACKGROUND OF THE INVENTION

Phospholipid biosynthesis in Saccharomyces cerevisiae is regulated in a coordinated fashion. Inositol 1-phosphate synthase [I1PS], Cytidine diphosphate diacylglycerol synthase [CDP-DGS], phosphatidylserine synthase [PSS], phosphatidylserine decarboxylase [PSD] and the phospholipid methyltransferases (PMTs) which convert phosphatidylethanolamine (PE) to phosphatidylcholine (PC), are all subject to regulation by inositol and choline (See FIG. 1). All of these enzymes show various degrees of repression in cells grown in the presence of inositol, and all display maximal repression When cells are grown in the presence of inositol and choline. However, the enzyme ultimately responsible for the production of PI, phosphatidylinositol synthase (PIS), is not regulated in response to phospholipid precursors.

Several of the phospholipid biosynthetic enzyme activities have been shown to be regulated at the level of transcription of structural genes. The steady-state levels of INOl mRNA and CHOI mRNA encoding for I1PS and PSS respectively, are reduced when wild type cells are grown in the presence of inositol. The mRNA levels are further reduced when both inositol and choline are present in the growth medium. A similar response has also been observed with the CHO2 and OP13 genes encoding the PMTs (See FIG. 1).

Several of the coregulated structural genes have also been shown to be controlled by a common set of regulatory genes. Many mutants with defects in the regulation of phospholipid metabolism were originally isolated on the basis of a defect in I1PS regulation. The wild-type products of the regulatory genes IN02 and IN04 are required for expression of IN01. Mutations at either of these two loci result in failure of cells to express I1PS, leading to inositol auxotrophy. The ino2 and ino4 mutants are also unable to derepress the entire set of enzymes that are subject to coordinate control by inositol and choline.

Mutants with lesions at the OPIl locus were originally isolated by Greenberg, M., Goldwasser, P., and Henry, S. (1982). Mol. Gen. Genet. 186, 157-163 and Greenberg, M. L., Reiner, B., and Henry, S. A. (1982). Genetics 100, 19-33 on the basis of an Over Production of Inositol Phenotype (Opi⁻). The opil mutants constitutively express derepressed levels of I1PS, as well as many of the other coregulated enzymes. The effect of the opil regulatory mutation is also apparent at the level of mRNA. In opil mutants, INOl transcript is constitutively overexpressed regardless of the growth condition. Thus, the opil gene, SEQ ID NO: 1; is believed to encode a negative regulatory factor that is required to repress the whole subset of enzymes that are coordinately controlled by inositol and choline.

Results from a deletion analysis of the 5' untranslated region of INOl show there are cis-acting regulatory sites that act to reduce transcription of this gene under repressing growth conditions. See Hirsch, J. P., Lopes, J. M., Chorgo, P. A., and Henry, S. A. (1991). Nucl. Acids Res. Submitted. In order to understand the mechanism by which the OPIl gene, SEQ ID NO: 1, and its product, SEQ ID NO: 2, interact with other regulatory genes and the structural genes under their control, a detailed molecular analysis of the OPIl gene, SEQ ID NO: 1, has been achieved. The present invention presents the genetic mapping, cloning and molecular analysis of the opil gene, SEQ ID NO: 1, and the use of it and its gene product, SEQ ID NO:2, in phospholipid biosynthesis to excrete excess inositol, for instance, for human or animal consumption.

SUMMARY OF THE INVENTION

The present invention pertains to a yeast cell, preferably Saccharomyces cerevisiae, which contains a functional stable recombinant DNA sequence that does not allow for the encoding of a negative regulator of phospholipid biosynthesis therein.

In a preferred embodiment, the recombinant DNA sequence is an opil gene deletion which results in the deregulation of inositol or inositol-containing metabolites such as inositol-1-phosphate synthase.

The present invention pertains to a method for obtaining inositol, inositol-containing metabolites or phospholipids such as myo-inositol or inositol-1-phosphate. The method comprises the steps of genetically engineering a stable yeast cell, preferably Saccharomyces cerevisiae, to continually produce inositol, inositol-containing metabolites or phospholipids. Additionally, there is the step of then generating the inositol, inositol-containing metabolites or phospholipids.

In a preferred embodiment, the genetically engineering step includes the step of altering the negative regulatory step involved in phospholipid biosynthesis to overproduce inositol, inositol-containing metabolites or phospholipids such as myo-inositol.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, the preferred embodiments of the invention and preferred methods of practicing the invention are illustrated in which:

FIG. 1 illustrates pathways for phospholipid biosynthesis in Saccharomyces cerevisiae.

FIG. 2 illustrates a bioassay for the Opil⁻ phenotype. Overproduction and excretion of inositol by strains results in the growth of the indicator strain around the patch of cells.

FIG. 3 illustrates restriction mapping, subcloning and complementation of the opi⁻ phenotype. Ability of subclones to complement opil mutant strains is indicated with a (+), inability to complement is indicated with a (-) and partial complementation is indicated with a (+/-).

FIG. 4 shows construction of opil disruption alleles.

FIG. 4a illustrates an insertion whereby a LEU2 selectable marker was inserted into the OPIl coding region (SEQ ID NO: 1).

FIG. 4b illustrates a deletion whereby the whole OPIl coding region was removed and replaced with a LEU2 selectable marker.

FIG. 5 illustrates Southern-blot analysis of opil disruption alleles. A ³² P-labelled nick-translated SstI-HindIII DNA fragment from pMW20 (FIG. 4b) was used to hybridize to the Southern blot.

FIG. 6 illustrates slot-blot analysis of INOl mRNA from opil mutant strains. Amounts of INOl mRNA were normalized to mRNA values obtained for ribosomal protein gene TCM1 and expressed relative to wild-type derepressed levels. All values are the means of three independent determinations.

FIG. 7 illustrates the sequency strategy. The arrows indicate the direction of ssDNA sequencing and the arrow labelled OPIl indicate the position of the OPIl coding region (SEQ ID NO: 1) and direction of transcription.

FIGS. 8a through 8f illustrate the nucleotide sequence, SEQ ID NO: 1, and predicted amino acid sequence, SEQ ID NO: 2, of the OPIl gene. The leucine residues of the leucine zipper are underlined and polyglutamine stretches are located within extended boxes. Positions of nonsense codons in isolated opil mutant allels are marked with an asterisk.

FIG. 9 illustrates deletions of the cloned OPIl gene. Ability to complement an opil mutation is indicated with a (+), inability to complement is indicated with a (-) and partial complementation is indicated with a (+/-).

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention pertains to a yeast cell, such as brewer's yeast or baker's yeast (Saccharomyces cerevisiae). The yeast cell contains a functional stable recombinant DNA sequence that does not allow for the encoding of a negative regulator of phospholipid biosynthesis therein. The recombinant DNA sequence preferably does not allow for the encoding of a negative regulator of inositol or inositol-containing metabolites.

Preferably, the recombinant DNA sequence is an OPIl gene deletion. The OPIl gene, SEQ ID NO: 1, encodes the negative regulator Opilp. Preferably, the OPIl gene has a nucleotide (SEQ ID NO: 1) and amino acid (SEQ ID NO: 2) sequence as shown in FIG. 8. The Opilp consists of 404 amino acid residues that has a molecular weight of 40,036. The Opilp contains polyglutamine tracks and a leucine zipper.

The present invention also pertains to a method for obtaining inositol, inositol-containing metabolites or phospholipids. The method comprises the steps of first genetically engineering a stable yeast cell to continually produce inositol, inositol-containing metabolites or phospholipids and then generating the inositol, inositol-containing metabolites or phospholipids. The yeast cell can be brewer's yeast or preferably baker's yeast, Saccharomyces cerevisiae as described herein.

A computer disc having the INOl and the OPIl (SEQ ID NO: 1) DNA sequences in computer readable form is included in Appendix A herein. The computer disc with the DNA sequences was produced from a Macintosh™ PC with the computer program titled Strider. Additionally, these DNA sequences are present in the GenBank™/EMBL database. The OPIl DNA sequence, SEQ ID NO: 1, can be accessed therethrough with access number M57383, and the INOl DNA sequence can be accessed therethrough with access number J04453. The Saccharomyces cerevisiae of the present invention are available at Carnegie Mellon University, Mellon Institute, Department of Biological Sciences and are available from American Type Culture Collection, under ATCC designation number 74033, where it was depositd on Feb. 13, 1991.

The following discloses the preferred materials and methods by which the OPIl gene (SEQ ID NO: 1) is mapped, cloned and molecularly analyzed, leading to the construction of a diploid opil deletion mutant. For routine bacterial transformations and maintenance of plasmids, Escherichia coli DH5α [F⁻, endA1,hsdR17(r_(k) -, m_(k) ⁺),supE44,thi-1, recA1, gyrA96, relA1, Δ (argF-lac zya) U169, φ80d lacZ Δ M15, λ⁻ ] (Hanahan, D., 1983). J. Mol. Biol. 166, 557--580 was used. While E. coli XL1-Blue [recA1,endA1,gyrA96,thi,hsdR17(r_(k) -, m_(k) +), supE44,relA1, λ⁻,lac⁻, {F',proAB,lacI^(Q),lacZ Δ 15, Tn10(tet^(R))}] (Bullock, W. O., Fernandez, J. M., and Short, J. M. 1987). Biotechniques 5, 376-379 is used for single stranded DNA (ssDNA) production.

The genotypes and sources of Saccharomyces cerevisiae strains used with respect to the OPIl are presented in Table 1.

The following growth media and genetic methods are also used; Escherichia coli DH5α cells used to propagate plasmid DNA were grown in LB medium containing 50 μgml⁻¹ ampicillin. Bacterial strain XL1-Blue used for the production of ssDNA is a lac⁻ AG1 derivative with Tn10, lacI^(Q), and lac Δ M15 on the F'. Selection for organisms containing F' is accomplished by addition of 10 μgml⁻¹ tetracycline to the above medium. Plates that have been spread with 50 μl 100 mM IPTG and 50 μl 2% (w/v) χ-gal in dimethylformamide are used to detect colonies with plasmids containing yeast genomic-DNA inserts. All bacterial strains are incubated at 37° C.

Media used for growth and sporulation of yeast have been described by Sherman, F., Fink, G. R., and Lawrence, C. W. (1978). In Methods Yeast Genetics, Cold Spring Harbor Laboratory, N.Y. For routine culture, YEPD medium (1% yeast extract, 2% peptone, 2% glucose) is used. The synthetic complete medium contained in (L⁻¹): glucose, 20 g; vitamin-free yeast nitrogen base (Difco), 6.7 g; biotin, 2 μg; calcium pantothenate, 400 μg; folic acid, 2 μg; niacin, 400 μg; p-aminobenzoic acid; 200 μg; pyridoxine hydrochloride, 400 μg; myo-inositol, 2 mg; lysine, 20 mg; arginine, 20 mg; methionine, 20 mg; threonine, 300 mg; tryptophan, 20 mg; leucine, 60 mg; histidine, 10 mg; adenine, 20 mg; uracil, 40 mg; and agar (for plates only), 20 g. Auxotrophic markers are checked on medium lacking a single component of the complete medium (drop-out medium). Inositol-free medium (I⁻¹) is identical to synthetic complete medium with the exception that myo-inositol has been omitted. As described by Ruby, S. W., Szostak, J. W., and Murray, A. W. (1983). Methods Enzymol. 101, 253-267, a buffered medium used to score β-galactosidase activity consists of all components of synthetic complete medium except vitamin-free yeast nitrogen base, with the addition of 0.1MKH₂ PO₄ (pH 7.0), 15 mM [NH₄ ]₂ S04, 0.8 mM MgSO₄ ·7H2O, 2 μM FeSO₄ ·6H₂ 0, 75 mM KOH, and 0.04 mgml⁻¹ χ-gal. Where indicated media is supplemented with 10 μM or 75 μM myo-inositol and/or 1 mM choline chloride. In all work involving S. cerevisiae, cultures are incubated at 30° C.

Bacterial strains were transformed with plasmid DNA following the calcium chloride procedure described by Mandel, M., and Higa, A. (1970). J.Mol. Biol. 53, 159-162. Yeast strains are transformed with isolated plasmid DNA using the lithium acetate method described by Ito, H., Yasuki, F., Murata, K., and Kimura, A. (1983). J. Bacteriol. 153, 163-168 and modified by Hirsch, J. P., and Henry, S. A. (1986). Mol. Cell. Biol. 6, 3320-3328. Where indicated, directed transformations and gapped-plasmid transformations are performed by digesting plasmids at specific endonuclease restriction sites.

The following methods are used to assay for Opi⁻ [Over Production of Inositol] phenotype:

1. Strains of S. cerevisiae are tested for the Opi⁻ phenotype by a modification of the method first described by Greenberg, M., Goldwasser, P., and Henry, S. (1982). Mol. Gen. Genet. 186, 157-163 and Greenberg, M. L., Reiner, B., and Henry, S. A. (1982). Genetics 100, 19-33.

2. Strains are patched into I⁻ plates and, after 24 h incubation, sprayed with a suspension of a tester strain (AID) in sterile distilled water. The tester strain is a diploid homozygous for an ade1 marker, which confers a red phenotype and an INOl marker, which confers inositol auxotrophy (Table 1). Overproduction and excretion of inositol by strains results in growth of the tester strain as seen by a red halo around the patch (See FIG. 2).

                  TABLE 1                                                          ______________________________________                                         List of S. cerevisiae strains used in this study                               Strain                                                                         designation  Genotype                                                          ______________________________________                                         AID          ade1/ade1 ino1/ino1 MATa/α                                  DC5          his3-11,15 leu2-3,-112 MATa                                       W303-1A      ade2-1 can1-100 his3-11,-15                                                    leu2-3,-112 trp1 ura3-1 MATa                                      WT1          leu2-3,-112 MATα                                            WT2          ade5 leu2-3,-112 MATα                                       JH0-6D       opi1-1 ade5 leu2-3,-112 trp1-1                                                 ura3-1 MATa                                                       JH2-3D       opi1-1 hom3 MATa                                                  JH2-7C       spo11 ade2 MATa                                                   NO80         opi1-2 his3-11,-15 leu2-3,-112                                                 MATa                                                              NO99         opi1-3 his3-11,-15 leu2-3,-112                                                 MATa                                                              OP1          opi1-1 lys2 MATα                                            OP12         opi1-12 lys2 MATα                                           OP-lacZ      opi1-1 ade5 leu2-3,-112 trp1-1                                                 URA3 (pJH334, INO1'lacZ)                                                       ura3-1 MATa                                                       OP-Δ1  opi1-::LEU2 leu2-3,-112 his3-11,                                  15 MATa                                                                        OP-Δ2  opi1-Δ::LEU2 leu2-3,-112 his3-11,                           15 MATa                                                                        DD1          opi1-::LEU2/OPI1 his3-11,-15/                                                  HIS3 leu2-3,-112/leu2-3,-112                                                   MATa/α                                                      DD2          opi1-::LEU2/opi1-1 his3-11,-15/                                                HIS3 leu2-3,-112/LEU2 LYS2/                                                    lys2 MATa/α                                                 DD3          opi1-::LEU2/opi1-12 his3-11,-15/                                               HIS3 leu2-3,-112/LEU2 LYS2/                                                    lys2 MATa/α                                                 ______________________________________                                    

3. Strains transformed with genomic DNA in high-copy shuttle vectors or centromeric are assayed using I⁻ plates lacking leucine or uracil.

The chromosomal mapping, cloning and subcloning of the OPIl gene (SEQ ID NO: 1) are done as follows:

1. The SPOll-maping technique described by Klapholtz, S., and Esposito, R. E. (1982). Genetics 100, 387-412 was chosen to map the OPIl locus.

a. This procedure utilizes the ability of diploid strains homozygous for the spo11-1 mutation to undergo chromosomal segregation without appreciable recombination during sporulation.

b. While constructing strains required for the SPOll-mapping technique, it was determined that the OPIl gene (SEQ ID NO: 1) and SPOll gene are on the same chromosome and not separable by recombination.

2. A 9.5 kilobase (kb) yeast genomic clone containing the SPOll gene, p(SPOll)1, was obtained from C. Atcheson and R. Esposito and used to transform an opil mutant strain (JH0-6D).

a. This 9.5 kb fragment has been cloned into the yeast centromeric plasmid YCp19, Stinchcomb, D. T., Mann, C., and Davis, R. W. (1982). J. Mol. Biol. 158, 157-179; (Table 2).

b. Two additional clones were obtained from C. Atcheson and R. Esposito that had been used to localize the SPOll gene and were tested for their ability to complement an opil mutation (See FIG. 3).

c. Plasmid p(SPOll]3 is a 4.0 kb BamHl-HindIII fragment from p(SPOll)1 cloned into YCp50, Johnston, M., and Davis, R. W. (1984). Mol. Cell. Biol. 4, 1440-1448 and p(SPOll)9 is a SalI digest of p(SPOll)1 religated (Table 2).

                  TABLE 2                                                          ______________________________________                                         List of plasmid constructions                                                  Plasmid    Subclone            Vector                                          ______________________________________                                         p(SPO11)1  9.5kb from yeast genomic                                                                           YCp19                                                      DNA                                                                 p(SPO11)3  4.0kb BamHI-HindIII from                                                                           YCp50                                                      p(SPO11)1                                                           p(SPO11)9  SalI digest/religation of                                                                          YCp19                                                      p(SPO11)1                                                           pJH334     1.0kb BglII-PstI 5' INO1                                                                           YIp357R                                                    DNA in frame with lacZ                                              pJH344     2.8kb BamHI-SalI from                                                                              YEp351                                                     p(SPO11)3                                                           pJH354     2.8kb SstI-HindIII from                                                                            YEp351                                                     p(SPO11)3                                                           pJH355     1.2kb BglII-HindIII from                                                                           YEp351                                                     p(SPO11)3                                                           pMW10      2.0kb XhoI-XhoI from                                                                               YEp352                                                     pJH354                                                              pMW11      2.0kb XhoI-XhoI from                                                                               YEp352                                                     pJH354 (opposite orientation)                                       pMW12      1.3kb EcoRV-HindIII from                                                                           YEp352                                                     pJH354                                                              pMW13      0.8kb EcoRV-HindIII from                                                                           YEp352                                                     pJH354                                                              pMW14      2.0kb SstI-PstI from pMW10                                                                         YIp351                                          pMW15      2.0kb SstI-PstI from pMW11                                                                         Ylp351                                          pMW16      3.0kb BglII-BglII LEU2 into                                                                        YEp351                                                     pMW10                                                               pMW17      3.0kb BglII-BglII LEU2 into                                                                        YEp352                                                     pMW10 (opposite orientation)                                        pMW18      3.0kb BglII-BglII LEU2 into                                                                        YEp352                                                     pMW11                                                               pMW19      3.0kb BglII-BglII LEU2 into                                                                        YEp352                                                     pMW11 (opposite orientation)                                        pMW20      2.2kb SalI-XhoI LEU2 into                                                                          YEp351                                                     XhoI-XhoI Δ of pJH354                                         pMW21      2.2kb SalI-XhoI LEU2 into                                                                          YEp351                                                     XhoI-XhoI Δ of pJH354                                                    (opposite orientation)                                              pMW22      1.5kb SpeI-XhoI from                                                                               YEp352                                                     pMW10                                                               pMW23      1.4kb NaeI-XhoI from                                                                               YEp352                                                     pMW10                                                               pMW24      1.0kb DraI-XhoI from                                                                               YEp352                                                     pMW10                                                               ______________________________________                                    

3. The yeast/E. coli shuttle vectors described by Hill, J. E., Myers, A. M., Koerner, T. J., and Tzagoloff, A. (1986). Yeast 2, 163-167 are used to construct additional subclones (Table 2).

a. The BamHI-SalI, SstI, HindIII and BglII-HindIII fragments from p(SPOll)3 are cloned into YEp351 to give pJH344, pJH354 and pJH355 respectively.

b. Fragment XhoI-XhoI from pJH354 is cloned in both orientations, into the SalI site of YEp352 to give plasmids pMW10 and pMW11.

c. The fragments EcoRV-HindIII and EcoRV-XhoI from pJH354 are cloned into the SmaI-HindIII and SmaI-SalI sites of YEp352 to give plasmids pMW12 and pMW13 respectively.

d. Cloned fragments of pMW10 and pMW11 are also cloned into YIp351, using the SstI-PstI sites of YEp352, to give plasmids pMW14 and pMW15 respectively (Table 2). All of these subclones are tested for their ability to complement the opil mutant phenotype (See FIG. 3).

Yeast strains carrying an INOl'lacZ fusion are constructed as follows. Mutations in the OPIl gene result in constitutive expression of the INOl gene. In order to obtain a plate phenotype based on the β-galactosidase assay, strains carrying a section of the INOl promoter fused to the lacZ reporter gene of E. coli are constructed. The integrating plasmid pJH334, [Hirsch, J. P., Lopes, J. M., Chorgo, P. A., and Henry, S. A. (1991). Nucl. Acids Res. Submitted; (See Table 2)] is used to transform yeast strains. This plasmid has been constructed from the lacZ-fusion vector YIp357R [Myers, A. M., Tzagoloff, A., Kinney, D. M., and Lusty, C. J. (1986). Gene 45, 299-310] and contains a 1.0 kb fragment of 5' INOl DNA fused in frame with lacZ. In previous studies, this fusion was shown to be fully regulated in response to inositol and choline and be expressed constitutively in an opil mutant background, Hirsch, J. P., Lopes, J. M., Chorgo, P. A., and Henry, S. A. (1991). Nucl. Acids Res. Submitted. Plasmid DNA that had been linearized at the URA3 selectable marker with Stul is used to transform Ura⁻ strains W303-1A and JH0-6D.

The opil-1 strain OP-lacZ (Table I) carrying a single copy of the INOl'lacZ fusion, is also transformed with plasmid pMW14 or pMW15. Each of these are directed to the OPIl locus by linearizing the plasmid at the BglII site. All transformants are tested for β-galactosidase activity using χ-gal plates with and without phospholipid precursors, inositol and choline.

The isolation of DNA and RNA is described below. Plasmid DNA is isolated from transformed bacterial strains either by the boiling miniprep method, originally described by Holmes, D. S., and Quigley, M. (1981). Anal. Biochem. 114, 193-197, or the CsCl-EtBr gradient procedure used by Clewell, D. B., and Helinski, D. R. (1969). Proc. Natl. Acad. Sci. U.S.A. 62, 1159-1166. Plasmids used for the preparation of sequencing templates are constructed by inserting agarose-gel purified OPIl restriction fragments, from plasmids pMW10 and pMW11, into the vector pGEM™-5Zf(+) [Promega Biotech; See FIG. 7]. For induction of ssDNA, E. coli XL1-Blue cells containing pGEM-5Zf(+) recombinants are infected with the helper phage M13K07 (Promega Biotech). Single-stranded DNA exported from bacterial cells as encapsidated virus-like particles is purified by simple precipitation and extraction procedures. Isolation of yeast-genomic DNA for Southern-blot analysis is performed using the method described by Hoffman, C. S., and Winston, F. (1987). Gene 57, 267-272. Total yeast RNA from organisms grown in the presence and absence of phospholipid precursors is isolated using the glass-bead disruption and hot-phenol extraction procedure of Elion, R. A., and Warner, J. R. (1984). Cell 39, 663-673.

The following methods are used to construct the opil disruption alleles:

1. Plasmids containing disrupted OPIl fragments are constructed using either pMW10/pMW11 or pJH354 (Table 2).

2. Plasmid pMW10 or pMW11 is linearized at the BglII site, which is internal to the cloned DNA, and a 3.0 kb BglII-BglII LEU2 gene-fragment from YEp13 is inserted in either orientation. This gives rise to plasmids pMW16, pMW17, pMW18 and pMW19 (Table 2).

3. Plasmid pJH354 is digested with the restriction endonuclease XhoI, so as to remove a 2.0 kb fragment from the cloned OPIl gene fragment, and a 2.2 kb SalI-XhoI LEU2 gene-fragment from YEp13 is inserted in either orientation, giving plasmids pMW20 and pMW21 [Table 2]. The opil gene-fragments containing the selectable LEU2 yeast gene is liberated from plasmids by cutting with SstI-HindIII (See FIGS. 4a and 4b) and used in a one-step disruption transformation of a haploid strain (DC5) wild-type for OPIl as described by Rothstein, R. J. (1983). Methods Enzymol. 101, 202-211.

The following methods are used to construct diploid OPIL disruption strains containing multiple insertions of the gene, INOl, encoding for inositol-1-phosphate synthesis.

Southern-blot analysis as taught by Southern, E. M. (1975). J. Mol. Biol. 98, 503-517 is done as follows. Yeast genomic DNA is digested for 6-7 hours with the appropriate restriction enzymes and analyzed by blot hybridization. Digested DNA is subjected to electrophoresis through a 1% (w/v) agarose gel in 89 mM Tris base-89 mM boric acid-2 mM EDTA (pH 8.0) (TBE) and transferred to nitrocellulose (0.45 μM poresize; S & S NC, Schleicher and Schuell, Inc.) as described by Maniatis, T., Fritsch, E. F. and Sambrook, J. (1982) in Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Laboratory, N.Y. Blots were prehybridized and ³² P-labelled nick-translated probes hybridized at 37° C. according to the procedure of Maniatis, et al. (1982).

Northern and slot-blot analysis are done as described below:

1. Total yeast RNA is fractionated on a 1.2% [W/V] agarose-3% (v/V) formaldehyde-20 mM 3-(N-morpholino) -propanesulfonic acid [pH 7.4]-1 mM EDTA gel and transferred to nitocellulose as described by Thomas, P. S. (1980). Proc. Natl. Acad. Sci U.S.A. 77, 5201-5205.

2. Slot blots of total yeast RNA are prepared using a Hybrilot slot-blot manifold [Bethesda Research Laboratories].

3. Total RNA [1,2 and 3 μg] is applied directly to nitrocellulose under high-salt conditions [3M Nacl, 0.3M Na₃ C₆ H₅ O₇.2H₂ O].

4. Northern blots and slot blots are prehybridized and ³² P-labelled ssRNA probes, synthesized using SP6 polymerase (Boehringer Mannheim Biochemicals), hybridized as described for Southern blots with the exception that the incubation temperature was 53° C.

5. Slot-blot hybridization signals are quantitated after a visual examination using Kodak X-Omat AR X-ray film [Eastman Kodak Company], by cutting out each slot and counting its radioactivity using a Beckman LS5801 liquid scintillation counter (Beckman Instruments, Inc.).

Single-stranded DNA templates are sequenced using the dideoxy chain-termination procedure first described by Sanger, F., Nicklen, S., and Coulsen, A. R. (1977). Proc. Natl. Acad. Sci. U.S.A. 74, 5463-5467. The universal M13 primer is annealed to ssDNA templates and DNA sequencing performed using a Sequenase kit [United States Biochemical Corp.]. The radionucleotide [α-³⁵ S] ATP (Amersham) is used in all labelling reactions. Routinely, 4-8% (W/V) polyacrylamide-7M urea wedge-gels (0.2-0.8 mm) are used and run on an IBI Standard Sequencer [Model STS 45; International Biotechnologies, Inc.) at a constant 80 watts. Sequencing gels are not fixed before exposure to X-ray film, but dried directly onto Whatman 3M filter paper as described by Kraft, R., Tardiff, J. Krauter, K. S. and Leinwand, L. A. (1988). Biotechniques 6, 544-547.

The DNA Strider program (version 1.0) and PC/Gene (version 6.01) are used for immediate analysis of the OPIl nucleotide and protein sequences. Both GenBank (version 60.0) and EMBL (version 18.0) libraries on BIONET were searched to find nucleotide sequences similar to that of OPIl (SEQ ID NO: 1). Protein databases NBRF-PIR (version 20.0) and SWISS-Prot (version 10.0) on BIONET were searched for protein sequences similar to the predicted polypeptide sequence of OPIl.

Plasmid-borne copies of several opil mutant alleles are obtained using the gap-repair procedure described by Orr-Weaver, T. L., Szostak, J. W., and Rothstein, R. J. (1983). Methods Enzymol. 101, 228-245. This technique utilizes the ability of yeast to repair gaps in cloned genes using information from chromosomal DNA. Thus, when a gapped plasmid is used to transform a strain harboring a mutant allele, and the deletion extends past the chromosomal mutation, the mutated sequence is copied onto the plasmid. Using the integrating plasmid pMW14 (Table 2), a series of four gapped plasmids are constructed that had sequences deleted from the OPIl coding region. These are a 141 bp SpeI-NaeI deletion, a 602 bp NaeI-BglII deletion, a 315 bp BglII-SalI deletion and a 194 bp SalI-NsiI deletion. Three opil mutant strains, JHO-6D, NO80 and NO99, are transformed with each of the four gapped-plasmids and all Leu⁺ transformats assayed for the Opi⁻ phenotype. Transformants that retained the Opi⁻ phenotype are assumed to have an integrated copy of the repaired gapped-plasmid, resulting in two copies of the gene each containing the mutant allele. Genomic DNA was isolated from several Leu⁺ Opi⁻ transformants, as previously described. By digesting 5-10 μg. of DNA with any restriction endonuclease that cut once within the cloned DNA and ligating under dilute conditions, plasmids containing the mutant alleles are re-isolated. Plasmids containing mutant alleles are amplified using the E. coli strain DH5α and the repaired gaps are subcloned into sections for ssDNA sequencing, as previously described.

The chromosomal mapping, cloning and localization of the OPIl gene, (SEQ ID NO: 1) is obtained as follows. The OPIl gene is assigned to a chromosomal map position to determine its location with respect to other genes involved in phospholipid biosynthesis. Crosses to strains bearing the spoll mutation, Klapholtz, S., and Esposito, R. E. (1982). Genetics 100, 387-412, indicated that the OPIl gene is tightly linked to SPOll on chromosome VIII. When a haploid strain carrying an opil-1 allele (JH2-3D) is crossed to a haploid strain containing a spoll-1 allele (JH2-7C) and the diploids sporulated, of 46 tetrads examined, 43 contain spores with the parental configuration (i.e., opil, SPOll or OPIl spoll). In these tetrads, the opil and SPOll alleles segregate 2⁺ :2⁻. The other three tetrads have a 3:1 segregation pattern for the opil mutation and are most likely a result of a gene conversion event at the OPIl locus. Thus, OPIl and SPOll are on the same chromosome and recombine with a frequency of less than 2%.

Three clones, p(SPOll)1, p(SPOll)3, and p(SPOll)9 that are used to localize the SPOll gene were generously provided by C. Atcheson and R. Esposito. See Atcheson, C. L., DiDomenico, B., Frankman, S., Esposito, R. E. and Elder, R. T. (1987). Proc. Natl. Acad. Sci. U.S.A. 84, 8035-8039. The ability of these clones to complement an opil mutation is shown in FIG. 3. Complementation studies reveal that the OPIl gene, SEQ ID NO: 1, is distinct from SPOll since plasmid p(SPOll)3, which does not complement spoll, complements opil and p(SPOll)9, which complements spoll, does not complement opil. The ATR1 (Adjacent Transcript 1) gene, unlike the SPOll gene, is not expressed during sporulation and its function is unknown. See Atcheson, C. L., DiDomenico, B., Frankman, S., Esposito, R. E. and Elder, R. T. (1987). Proc. Natl. Acad. Sci. U.S.A. 84, 8035-8039. Further subcloning of p(SPOll)1 eliminates the possibility that the ATR1 RNA encoded the OPIl gene product (FIG. 3). Approximately half of the ATR1 transcription unit is deleted in p(SPOll)3 and yet this clone fully complements the opil⁻ phenotype. Furthermore, complementation of the opil lesion is also observed with plasmid pJH354, demonstrating that the leftmost 1.8 kb BamHI-SstI fragment is not required for OPIl function. Plasmid pMW12, which includes about 0.6 kb of sequence upstream of the ATR1 initiation site, does not complement the opil⁻ phenotype. Plasmid pJH344, which does not include any of the ATR1 transcription unit, is capable of partial complementation, and the 2.0 kb XhoI-XhoI fragment (pMW10 or pMW11) which includes only a few hundred bases downstream of the ATR1 transcription start site, fully complements the opil lesion. Plasmids pMW10 and pMW11 contain (in opposite orientations) the smallest subclone that complements opil (See FIG. 3). Since either orientation of the smallest subclone is capable of complementation, the fragment most contains the entire OPIl coding and promoter sequences. Complementation studies show that the OPIl gene is in fact distinct from SPOll as well as closely located gene, ATR1.

Integration of the cloned DNA, disruption of the chromosomal opil locus (SEQ ID NO: 1) and genetic analysis of the OPIl insertion allele are accomplished as follows: The 2.0 kb OPIl fragment contained on plasmids pMW10 and pMW11 is also capable of complementing an opil mutation in single copy. Integrating plasmids pMW14 and pMW15 (See FIG. 3 and Table 3), each containing the 2.0 kb OPIl fragment in an opposite orientation are linearized at a unique BglII site (See FIG. 3) and used in a directed transformation of an opil mutant strain JHO-6D. Transformants are selected on the basis of leucine prototrophy and subsequently assayed for the opil⁻ phenotype as described before (See FIG. 2). Southern-blot analysis of genomic DNA confirms single-copy integrants. Complementation of the opil lesion by a single-integrated copy of the OPIl clone eliminates the possibility that a suppression carried in a high-copy plasmid may have been responsible for complementation by suppressing the opil⁻ phenotype.

                  TABLE 3                                                          ______________________________________                                         The cloned DNA complements the Opi1.sup.- phenotype and                        restores INO1's response to phospholipid precursors                                       INO1'lacZ I.sup.+ C.sup.+  +                                                                      I.sup.- C.sup.-  +                                                                    Excretion                                 Yeast Genotype                                                                            Fusion    X-gal    X-gal  of Inositol                               ______________________________________                                         OPI1       -         white    white  -                                         opi1-1     -         white    white  +                                         opi1-1 + pMW14                                                                            -         white    white  -                                         opi1-1 + pMW15                                                                            -         white    white  -                                         OPI1       +         light blue                                                                              dark blue                                                                             -                                         opi1-1     +         dark blue                                                                               dark blue                                                                             +                                         opi1-1 + pMW14                                                                            +         light blue                                                                              dark blue                                                                             -                                         opi1-1 + pMW15                                                                            +         light blue                                                                              dark blue                                                                             -                                         ______________________________________                                          I.sup.+ C.sup.+  corresponds to 75 μM inositol and 1 mM choline, the        repressed growth condition. I.sup.- C.sup.-  indicates absence of              supplements, the derepressed growth condition. Xgal,                           5Bromo-4-Chloro-3-Indolyl D-Galactopyranoside.                           

Insertion and deletion mutations (Table 2) are first constructed in autonomously-replicating plasmids, as described previously. Disruption of the cloned DNA is confirmed by transforming opil mutant strains with either plasmid pMW16 [containing an insertion of the LEU2 gene into the smallest OPIl subclone] or pMW20 (containing a deletion of the OPIl sequence with an insertion of the LEU2 gene). These plasmids fail to complement an opil mutation. To determine the phenotype of a disruption mutation at the genomic OPIl locus, cloned DNA fragments from pMW16 and pMW20 are used in a one-step disruption transformation of a Leu2⁻ haploid strain wild-type for OPIl (See FIGS. 4a and 4b). Leu⁺ transformants, in both cases, overproduce and excrete inositol giving a similar phenotype to existing opil alleles in the Opi⁻ test (See FIG. 2). Integration of the disrupted OPIl-gene fragments at the OPIl locus by homologous recombination is confirmed by Southern-blot analysis (See FIG. 5).

A strain containing the insertion-disruption allele opil-::LeU2 (strain OP-Δ1; Table 1) is crossed with two OPIl strains and two strains containing different opil alleles, opil-1 (OP1) and opil-12 (OPI12). Diploids are first tested for their ability to excrete inositol (See FIG. 2). Diploid strains heterozygous for the OPIl wild-type allels and the opil-::LEU2 allele exhibit an Opi⁺ phenotype whereas diploids produced by crossing haploid strains carrying the opil-1 or opil-12 alleles to strains carrying the opil disruption alleles have an Opi⁻ phenotype. Dissection of tetrads from the opil/opil⁻ ::LEU2 diploid give the expected 2⁺ :2⁻ segregation of the Opi⁺ :Opi⁻ phenotype. With the exception of two tetrads out of 55, Leu⁺ co-segregates with the Opi⁻ phenotype (Table 4). Tetrads from crosses involving strains containing either an opil-1 or opil-12 allele with the strain carrying an opil-::LEU2 allele show a 0⁺ :4⁻ segregation pattern of Opi⁺ :Opi⁻. Since the strain carrying the opil::LEU2 allele still contains a mutant LEU2 allele, a two-gene segregation pattern of Leu⁺ :Leu⁻ is observed (Table 4). These results confirm that the inserted DNA is linked to the OPIl locus and not to the LEU2 locus. Since a one-step gene-disruption transformation is successfully performed in a haploid strain wild-type for OPIl, this indicates that OPIl is not an essential gene, and removal of its function is not lethal to the organism.

                  TABLE 4                                                          ______________________________________                                         Genetic analysis of an opi1 insertion allele confirming                        that the cloned gene is OPI1                                                                                         Co-segre-                                            No of                     gation                                               tetrads Opi.sup.+ /       of Opi.sup.-                                         dis-    Opi.sup.-                                                                              Leu.sup.+ /Leu.sup.-                                                                     and                                      Cross       sected  2:2   0:4 2:2 1:3 3:1 4:0 Leu.sup.+                        ______________________________________                                         opi1-::LEU2 his3 ×                                                                   27      27    0   26  1   0   0   53/54                            WT1 leu2                                                                       opi1-::LEU2 his3 ×                                                                   28      28    0   27  1   0   0   55/56                            WT2 ade5 leu2                                                                  opi1-::LEU2 his3 ×                                                                   26      0     26  0   0   12  14  not                              opi1-1 lys2                                   relevant                         opi1-::LEU2 his3 ×                                                                   30      0     30  1   0   19  10  not                              opi1-12 lys2                                  relevant                         ______________________________________                                    

The data shows that the opil insertion-disruption allele expresses derepressed levels of INOl mRNA constitutively. In order to confirm that the opil gene disruption strains have a phenotype similar to opil mutants previously isolated, levels of INOl mRNA are analyzed in strains carrying the opil-::LEU2 allele grown under derepressing and repressing growth conditions (See FIG. 6). Slot blots of total RNA are probed with a ³² P-labeled INOl specific riboprobe generated from plasmid pJH320, Hirsch, J. P., and Henry S. A. (1986). Mol. Cell. Biol. 6, 3320-3328. The amounts of INOl mRNA are normalized to mRNA values obtained for the ribosomal protein gene TCM1, (Fried, H. M., and Warner, J. R. (1981). Proc. Natl. Acad. Sci. U.S.A. 78, 238-242) to correct for differences in RNA loadings, and expressed relative to wild-type derepressed levels. Strains wild-type for the OPIl gene regulate the level of INOl mRNA in response to soluble phospholipid precursors (See FIG. 6). These data on expression of INOl in wild type and opil strains are consistent with the data previously reported by, Hirsch, J. P., and Henry, S. A. (1986). Mol. Cell. Biol. 6, 3320-3328. In the strain carrying the opil-::LEU2 allele INOl transcription is constitutively derepressed in a manner similar to that found in the strain containing the opil-1 allele (See FIG. 6). Both opil mutant strains display a two- to three-fold increase in INOl mRNA as compared to wild-type derepressed levels. Thus the phenotype of mutants carrying the insertion-disruption allele at the OPIl locus is identical to the phenotype of previously described opil mutants with regard to overproduction of inositol and INOl expression (See FIG. 2 and FIG. 6).

It was found that the cloned DNA restores regulation of the INOl structural gene in an opil background, Yeast strains carrying an integrated copy of an INOl'lacZ fusion, as described previously, (See Hirsch, J. P., Lopes, J. M., Chorgo, P. A., and Henry, S. A. (1991). Nucl. Acids Res. Submitted.) were analyzed for their response to phospholipid precursors (Table 3). A strain wild-type for opil expressed β-galactosidase activity under derepressing growth conditions, as seen by a dark blue phenotype on χ-gal plates. Under repressing growth conditions (I⁺ C⁺) this strain has a light-blue phenotype indicating a basal/repressed level of β-galactosidase activity. The opil mutant carrying the INOl'lacZ fusion (OP-lacZ; Table 1) expresses derepressed levels of β-galactosidase, under derepressing and repressing growth conditions. The opil mutant containing an INOl'lacZ fusion, when transformed with either pMW14 or pMW15 results in the ability of the INOl promoter to respond to repressing and derepressing growth conditions. All transformants that appeared to have restored INOl regulation are tested for overproduction of inositol (Table 3). Complementation of the Opil⁻ phenotype coincided with the restoration of INOl's response to phospholipid precursors.

The nucleotide-sequence analysis and identification of the OPIl coding region, SEQ ID NO: 1, are done as follows: The nucleotide sequence of the 2 kb OPIl-complementing fragment is determined using the sequencing strategy shown in FIG. 7. An open reading frame (ORF) of 1212 bp is identified, starting with an ATG codon at nucleotide 439 and terminating with TAA codon at position 1650 (See FIGS. 8a-8f). Within this ORF there are three other potential translational start sites located at nucleotides 565, 829 and 1093 (See FIGS. 8a-8f). Computer analysis identified two other ORF's greater than 200 bp in the opposite strand. However, these do not coincide with the position of the LEU2 gene insertion (See FIG. 4a) and are therefore eliminated from further consideration. The cloned OPIl gene is further subcloned using unique restriction sites identified by sequence analysis (See FIG. 9). Three 5' deletions of the complementing XhoI-XhoI fragment are cloned into YEp352 to generate plasmids pMW22, pMW23 and pMW24 (Table 2). Plasmids pMW23 and pMW24 fail to complement an opil mutation because they are unable to encode the complete OPIl protein (Opilp). Plasmid pMW22, however, partially complements the Opil⁻ phenotype, as seen by a small excretion ring in the Opi⁻ test. This clone contains 10 untranslated nucleotides upstream of the first ATG (See FIGS. 8a-8f and 9). This may suggest that the complete OPIl gene product is translated from the sequence contained on pMW22. It is, however, possible that one of the downstream ATGs is used as the start codon, however, the data available does suggest that the ATG at nucleotide 439 is the translation initiation site for Opilp.

Strains bearing the opil mutant alleles, opil-1 (JHO-6D), opil-2 (NO80) and opil-3 (NO99), are transformed with the gapped plasmids described above. This analysis reveals that the mutations contained in all three strains lie within the same small stretch of DNA. Strains transformed with the gapped plasmids containing SpeI-NaeI, NaeI-BglII or SalI-NsiI deletions exhibit a complemented, Opi⁺, phenotype. The gaps in these plasmids do not extend past the chromosomal mutation. When strains are transformed with the BglII-SalI gapped plasmid, all retain the Opi⁻ phenotype. Failure of this construct to rescue any of the mutant alleles indicates that, in each case, the mutation must lie between the BglII and the SalI restriction sites of the OPIl locus. Sequencing of EcoRV-SalI fragments from re-isolated gapped plasmids (See FIG. 3) identifies nonsense mutations in each of the three alleles, all located within the first polyglutamine stretch of amino acid residues. Alleles opil-3 and opil-2 have a "TAA" codon located at nucleotide 1294 and 1312 respectively, whereas strain opil-1 has a "TAG" codon at nucleotide 1315 (See FIGS. 8a-8f).

The Opil protein is analyzed as follows: Translation of the OPIl ORF predicts a protein (Opilp) composed of 404 amino acids (SEQ ID NO: 2) (See FIGS. 8a-8f) with a molecular weight of 40,036. Opilp is a fairly acidic protein having an isoelectric point of 4.77. The codon bias produced for Opilp using the method of Bennetzen, J. L., and Hall, B. D. (1982). J. Biol. Chem. 257, 3026-3031, was 0.089, indicating that the OPIl gene product is a low-abundance protein Bennetzen, J. L., and Hall, B. D. (1982). J. Biol. Chem. 257, 3026-3031; Sharp, P., Tuhoy, T., and Mosurski, K. (1986). Nucl. Acids Res. 14, 5125-5143. This is consistent with the fact that Opilp is a regulatory protein. Hydropathicity analysis, Kyte, J., and Doolittle, K. F. (1982). J. Mol. Biol. 157, 105-132, of Opilp indicates no substantial hydrophobic regions suggesting that there are no membrane spanning regions. A heptad repeat of leucine residues (leucine zipper) is identified in the amino-acid sequence, starting at nucleotide 853 (See FIGS 8a-8f).

In a structural analysis of several proteins that are involved in gene regulation, Landschulz, W. H., Johnson, P. F., and McKnight, S. L. (1988). Science 240, 1759-1764, identified a leucine zipper encoded in the yeast transcriptional regulatory gene, GCN4, and the mammalian enhancer binding protein, C/EBP, as well as the proto-oncogene products belonging to the Jun, Fos, and Myc family of nuclear transforming proteins. This structure forms a stable α-helix whereby the leucines, repeated every seventh residue, form a hydrophobic spine down one face of the helix. The dimerization of monomer is stabilized by hydrophobic interactions between closely opposed α-helical leucine repeats, Landschulz, W. H., Johnson, P. F., and McKnight, S. L. (1988). Science 240, 1759-1764. The formation of these protein complexes is involved in the juxtapositioning of basic domains, or other DNA-binding domains, that facilitate binding of the protein to DNA. When represented in the form of helical structure the Opilp leucine zipper region exhibits amphipathicity that is consistent with many of the aforementioned DNA-binding proteins. The leucine residues of the zipper align down one face every second turn of the α-helix, while immediately opposite is a preponderance of amino-acid residues having either charged or uncharged polar side-chains. In addition, there are more hydrophobic residues that lie adjacent to the leucine residues at three out of four positions. It is believed that these adjacently positioned hydrophobic residues may add to the stability of hetero- or homo-dimers in the form of a coiled coil. (See Gentz, R., Rauscher, F., J., III, Abate, C., and Curran, T. (1989). Science 243, 1695-1699; Landschulz, W. H., Johnson, P. F., and McKnight, S. L. (1989). Science 243, 1681-1688; O'Shea, E. K., Rutkowski, R., and Kim, P. S. (1989a). Science 243, 538-542; O'Shea, R. K., Rutkowski, R., Stafford, W., F., III, and Kim, P. S. (1989b). Science 245, 646-648; Ransone, L. J., Visvader, J., Sassone-Corsi, P., and Verma, I. M. (1989). Genes Devel. 3, 770-781; Smeal, T., Angel, P., Meek, J., and Karin, M. (1989). Genes Devel. 2091-2100).

Immediately NH₂ -terminal to the Opilp leucine zipper is a 30 amino-acid residue region that contains a net basic charge. The basic domain is directly involved in protein-DNA binding and, together, the leucine zipper and basic domain are implicated as having a role in some DNA-binding proteins that regulate transcription. (See Landschulz, W. H., Johnson, P. F., and McKnight, S. L. (1988). Science 240, 1759-1764; Landschulz, W. H., Johnson, P. F., and McKnight, S. L. (1989). Science 243, 1681-1688; Brendel, V., and Karlin, S. (1989). Proc. Natl. Acad. Sci. U.S.A. 86, 5698-5702; Kouzarides, T., and Ziff, E. (1989). Nature 340, 568-571; Vinson, C. R., Sigler, P. B., and McKnight, S. L. (1989). Science 246, 911-916).

Based on the identification of cis-acting regulatory elements in the 5'promoter region on INOl, Hirsch, J. P., Lopes, J. M., Chorgo, P. A., and Henry, S. A. (1991). Nucl. Acids Res., Submitted, has employed DNA-binding/mobility-shift assays along with oligonucleotide competition experiments to assess the possible interaction of DNA-binding proteins with the INOl promoter. Using protein extracts from cells wild-type for OPIl as well as extracts from strains carrying the disruption alleles, an OPIl-dependent protein-DNA complex has been identified. When these studies are repeated using extracts from a strain carrying the opil-1 allele transformed with the cloned OPIl gene, the protein-DNA complex reappears. That Opilp contains a well defined leucine zipper and associated basic domain makes it a DNA-binding repressor protein that binds directly to the INOl promoter, and the promoter of other structural genes involved in the phospholipid biosynthetic pathway. Opilp may either dimerize with itself in the form of a coiled coil, similar to the yeast transcriptional activator encoded by GCN4, Kouzarides, T., and Ziff, E. (1989). Nature 340, 568-571; O'Shea, E. K., Rutkowski, R., and Kim, P. S. (1989). Science 243, 538-542, or complexes with another protein to form a heterodimer, similar to the c-jun and c-fos proto-oncogene products, Kouzarides, T., and Ziff, E. (1989). Nature 340, 568-571; Ransone, L. J., Visvader, J., Sassone-Corsi, P., and Verma, I. M. (1989). Genes Devel. 3, 770-781.

Two polyglutamine-residue stretches are also found in the translated OPIl sequence, SEQ ID NO: 2, starting at nucleotides 1294 and 1567 (See FIGS. 8a-8f). One consists of 21 glutamine resides with two intervening leucine doublets, and a smaller one of 9 glutamine residues is interrupted by a single tyrosine and arginine residue. Searching the nucleotide- and protein-sequence databases identified several genes with similarities to OPIl. However, this was due in large to the presence of sequences encoding polyglutamine residues. It is striking that glutamine-rich regions and polyglutamine tracts are being reported in an increasing number of predicted yeast proteins that have regulatory functions. When Opilp is analyzed using the FLEXPRO program in PC/GENE (version 6.01) the polyglutamine tracts are predicted to confer flexibility to the protein. This property may be involved in the orientation of binding domains to specific sites on DNA and/or other DNA-binding proteins, Bohmann, D., Bos, T. J., Admon, A., Nishimura, T., Vogt, P. K., and Tijan, R. (1987). Science 238, 1386-1392; Brendel, V., and Karlin, S. (1989). Proc. Natl. Acad. Sci. U.S.A. 86, 5698-5702. The opil nonsense mutations and the opil insertion-disruption mutation all truncate Opilp, removing the polyglutamine tracts. This causes the disappearance of an OPIl-dependent DNA-protein complex involving the INOl promoter possibly implicating a role for this structural motif in DNA binding. This interpretation is further supported by the fact that plasmid pJH344 (See FIG. 3), which contains the first long stretch of polyglutamine-residues but has the most carboxy-terminal stretch deleted, partially complemented an opil mutation.

The nucleotide sequence of OPIl (SEQ ID NO: 1) has identified a gene product that has properties consistent with its predicted role as a DNA-binding protein. The finding that Opilp possesses structural motifs, such as a leucine zipper and polyglutamine tracts (See FIGS. 8a-8f), that are found in a wide variety of DNA-binding proteins is a particularly significant one.

Although the invention has been described in detail in the foregoing embodiments for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be described by the following claims.

    __________________________________________________________________________     SEQUENCE LISTING                                                               (1) GENERAL INFORMATION:                                                       (iii) NUMBER OF SEQUENCES: 2                                                   (2) INFORMATION FOR SEQ ID NO:1:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 1897 base pairs                                                    (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: double                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE:                                                            (A) DESCRIPTION: Genomic DNA with translated open-reading                      frame containing the putative Opil protein                                     (iii) HYPOTHETICAL: No                                                         (iv) ANTI-SENSE: No                                                            (vi) ORIGINAL SOURCE:                                                          (A) ORGANISM: Saccharomyces cerevisiae                                         (B) STRAIN: Generic laboratory strain                                          (vii) IMMEDIATE SOURCE:                                                        (A) LIBRARY: YCp19 Library                                                     (B) CLONE: p(SPO11)1                                                           (viii) POSITION IN GENOME:                                                     (A) CHROMOSOME/SEGMENT: Chromosome VIII                                        (B) MAP POSITION: Adjacent to SPO11                                            (ix) FEATURE:                                                                  (A) NAME/KEY: OPI1 Gene                                                        (B) LOCATION: GenBankTM/EMBL Data Bank. Accession                              number J05727                                                                  (C) IDENTIFICATION METHOD: OPI1 gene was cloned using the                      SPO11 mapping technique. The cloned gene complemented an                       opil mutant strain.                                                            (D) OTHER INFORMATION: The cloned OPI1 gene restored INO1                      regulation in an opil mutant strain resulting in the loss                      of overproduction of inositol.                                                 (x) PUBLICATION INFORMATION:                                                   (A) AUTHORS: Michael J. White                                                  Jeanne P. Hirsch                                                               Susan A. Henry                                                                 (B) TITLE: The OPI1 Gene of Saccharomyces cerevisiae, a                        Negative Regulator of Phospholipid Biosynthesis,                               Encodes a Protein Containing Polyglutamine                                     Tracts and a Leucine Zipper                                                    (C) JOURNAL: The Journal of Biological Chemistry                               (D) VOLUME: 266                                                                (E) ISSUE: 2                                                                   (F) PAGES: 863-872                                                             (G) DATE: 15-1-91                                                              (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 1:                                       CTCGAGATAAGTTGGTCAACATTGATTTCGAGATTCCG38                                       TACTGTACATGCAGTGGCCTGAAAGTTGAGTACTTGAAGGTCGAAGAGCC88                           ACAATTGCAGTACCAGTCTTTCCCCTGGGTCAGATACAAGACCGTCAGCG138                          ACGAAGAGTACGCATATATTGTTTGACGCTTACGCAGACATCTCATAGAT188                          AGACAAATGGTACGTTCGTTTTAGTATATAGATGGCACCTTATAATCTTC238                          ATATGCAACCGGGTAAAATCGGGCGTTCTTATTTTTTTTTTTTCCACCTC288                          AATGAGAGGGATTAATAAGAGGATTGGAGCAAGACAGCGATCTGCACTTA338                          GCCAAGAAAGCATATCAGGCCAGAACGTGGCATTTTGTTTACAGTGCTGA388                          TTAAAGCGTGTGTATCAGGACAGTGTTTTTAACGAAGATACTAGTCATTG438                          ATGTCTGAAAATCAACGTTTAGGATTATCAGAGGAAGAGGTAGAA483                               MetSerGluAsnGlnArgLeuGlyLeuSerGluGluGluValGlu                                  051015                                                                         GCGGCTGAAGTACTTGGGGTGTTGAAACAATCATGCAGACAGAAG528                               AlaAlaGluValLeuGlyValLeuLysGlnSerCysArgGlnLys                                  202530                                                                         TCGCAGCCTTCAGAGGACGTCTCACAAGCTGACAAAATGCCGGCA573                               SerGlnProSerGluAspValSerGlnAlaAspLysMetProAla                                  354045                                                                         AGTGAGTCGTCTACGACGCCGCTAAACATTTTGGATCGCGTAAGT618                               SerGluSerSerThrThrProLeuAsnIleLeuAspArgValSer                                  505560                                                                         AACAAAATTATCAGTAACGTAGTGACATTCTACGATGAAATAAAC663                               AsnLysIleIleSerAsnValValThrPheTyrAspGluIleAsn                                  657075                                                                         ACCAACAAGAGGCCACTGAAATCAATAGGGAGGCTGCTAGACGAT708                               ThrAsnLysArgProLeuLysSerIleGlyArgLeuLeuAspAsp                                  808590                                                                         GACGATGACGAGCATGATGATTACGACTACAACGACGATGAGTTC753                               AspAspAspGluHisAspAspTyrAspTyrAsnAspAspGluPhe                                  95100105                                                                       TTCACCAACAAGAGACAGAAGCTGTCGCGGGCGATTGCCAAGGGG798                               PheThrAsnLysArgGlnLysLeuSerArgAlaIleAlaLysGly                                  110115120                                                                      AAGGACAACTTGAAAGAGTACAAGCTGAACATGTCCATCGAGTCT843                               LysAspAsnLeuLysGluTyrLysLeuAsnMetSerIleGluSer                                  125130135                                                                      AAGAAGAGGCTTGTAACGTGCTTGCATCTTTTAAAGCTGGCCAAT888                               LysLysArgLeuValThrCysLeuHisLeuLeuLysLeuAlaAsn                                  140145150                                                                      AAGCAGCTTTCCGATAAAATCTCGTGTTTACAGGACCTTGTTGAA933                               LysGlnLeuSerAspLysIleSerCysLeuGlnAspLeuValGlu                                  155160165                                                                      AAGGAGCAGGTGCATCCTTTGCACAAGCAAGATGGAAATGCTAGG978                               LysGluGlnValHisProLeuHisLysGlnAspGlyAsnAlaArg                                  170175180                                                                      ACGACCACTGGAGCTGGCGAGGACGAGACATCGTCAGACGAAGAC1023                              ThrThrThrGlyAlaGlyGluAspGluThrSerSerAspGluAsp                                  185190195                                                                      GACGACGATGAGGAGTTTTTTGATGCCTCAGAGCAGGTCAACGCC1068                              AspAspAspGluGluPhePheAspAlaSerGluGlnValAsnAla                                  200205210                                                                      AGCGAGCAGTCTATTGTGGTGAAAATGGAGGTGGTCGGCACAGTC1113                              SerGluGlnSerIleValValLysMetGluValValGlyThrVal                                  215220225                                                                      AAGAAAGTCTACTCGCTGATATCGAAGTTCACAGCAAATTCGCTG1158                              LysLysValTyrSerLeuIleSerLysPheThrAlaAsnSerLeu                                  230235240                                                                      CCGGAGCCCGCAAGATCTCAGGTTCGGGAAAGTCTTCTAAACTTA1203                              ProGluProAlaArgSerGlnValArgGluSerLeuLeuAsnLeu                                  245250255                                                                      CCCACAAATTGGTTCGACAGCGTCCACAGTACATCACTGCCGCAT1248                              ProThrAsnTrpPheAspSerValHisSerThrSerLeuProHis                                  260265270                                                                      CATGCTTCGTTTCATTATGCCAACTGTGAAGAACAAAAAGTGGAG1293                              HisAlaSerPheHisTyrAlaAsnCysGluGluGlnLysValGln                                  275280285                                                                      CAACAGCAACAGCAACAGCAACAGCAGCAGCAGCAGCAACTTTTG1338                              GlnGlnGlnGlnGlnGlnGlnGlnGlnGlnGlnGlnGlnLeuLeu                                  290295300                                                                      CAGCAGCAACTCCTGCAACAGCAACAGCAAAAAAGGAACAAGGAT1383                              GlnGlnGlnLeuLeuGlnGlnGlnGlnGlnLysArgAsnLysAsp                                  305310315                                                                      GGCGACGACTCAGCCTCGCCGTCCTCCTCCGTAACTGCGAATGGG1428                              GlyAspAspSerAlaSerProSerSerSerValThrAlaAsnGly                                  320325330                                                                      AAAGTACTCATTCTCGCCAAAGAATCCCTGGAAATGGTGAGAAAT1473                              LysValLeuIleLeuAlaLysGluSerLeuGluMetValArgAsn                                  335340345                                                                      GTCATGGGCGTAGTCGACTCCACGTTGGGCAAGGCTGAAGAATGG1518                              ValMetGlyValValAspSerThrLeuGlyLysAlaGluGluTrp                                  350355360                                                                      GTGAAGCAGAAACAGGAGGTAAAAGAAATGATCAGGGAGCGTTTC1563                              ValLysGlnLysGlnGluValLysGluMetIleArgGluArgPhe                                  365370375                                                                      TTGCAACAGCAGCAACAGTACAGGCAGCAACAGCAGAAGGATGGC1608                              LeuGlnGlnGlnGlnGlnTyrArgGlnGlnGlnGlnLysAspGly                                  380385390                                                                      AATTACGTAAAGCCCTCTCAGGACAACGTGGATAGCAAGGACTAA1653                              AsnTyrValLysProSerGlnAspAsnValAspSerLysAsp                                     395400                                                                         CCGAGACAGATTGAGGTCTTTCATGCATTACCACCAGTAATAATATTATA1703                         CGGAATAATATAGTTTATATAATATCCATAATCATAATCATAATCATAAT1753                         CATAATCATAATCGTGATATTGTACCAGCCCCGCTTCTCCCCTTTTGAAC1803                         TACCATTATTATCGGACCCTCTTTACCTTTGAATGGCTCAGTAAGGACCT1853                         TTGCGCGCCGTAAGGGGGTCGGGAATACATTTCCGGGGTTGATC1897                               (2) INFORMATION FOR SEQ ID NO:2:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 404 amino acids                                                    (B) TYPE: amino acid                                                           (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: Protein                                                    (iii) HYPOTHETICAL: Yes                                                        (x) PUBLICATION INFORMATION:                                                   (A) AUTHORS: Michael J. White                                                  Jeanne P. Hirsch                                                               Susan A. Henry                                                                 (B) TITLE: The OPI1 Gene of Saccharomyces cerevisiae, a                        Negative Regulator of Phospholipid Biosynthesis,                               Encodes a Protein Containing Polyglutamine                                     Tracts and a Leucine Zipper                                                    (C) JOURNAL: The Journal of Biological Chemistry                               (D) VOLUME: 266                                                                (E) ISSUE: 2                                                                   (F) PAGES: 863-872                                                             (G) DATE: 15-JAN-91                                                            (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 2:                                       MetSerGluAsnGlnArgLeuGlyLeuSerGluGluGluValGlu                                  151015                                                                         AlaAlaGluValLeuGlyValLeuLysGlnSerCysArgGlnLys                                  202530                                                                         SerGlnProSerGluAspValSerGlnAlaAspLysMetProAla                                  354045                                                                         SerGluSerSerThrThrProLeuAsnIleLeuAspArgValSer                                  505560                                                                         AsnLysIleIleSerAsnValValThrPheTyrAspGluIleAsn                                  657075                                                                         ThrAsnLysArgProLeuLysSerIleGlyArgLeuLeuAspAsp                                  808590                                                                         AspAspAspGluHisAspAspTyrAspTyrAsnAspAspGluPhe                                  95100105                                                                       PheThrAsnLysArgGlnLysLeuSerArgAlaIleAlaLysGly                                  110115120                                                                      LysAspAsnLeuLysGluTyrLysLeuAsnMetSerIleGluSer                                  125130135                                                                      LysLysArgLeuValThrCysLeuHisLeuLeuLysLeuAlaAsn                                  140145150                                                                      LysGlnLeuSerAspLysIleSerCysLeuGlnAspLeuValGlu                                  155160165                                                                      LysGluGlnValHisProLeuHisLysGlnAspGlyAsnAlaArg                                  170175180                                                                      ThrThrThrGlyAlaGlyGluAspGluThrSerSerAspGluAsp                                  185190195                                                                      AspAspAspGluGluPhePheAspAlaSerGluGlnValAsnAla                                  200205210                                                                      SerGluGlnSerIleValValLysMetGluValValGlyThrVal                                  215220225                                                                      LysLysValTyrSerLeuIleSerLysPheThrAlaAsnSerLeu                                  230235240                                                                      ProGluProAlaArgSerGlnValArgGluSerLeuLeuAsnLeu                                  245250255                                                                      ProThrAsnTrpPheAspSerValHisSerThrSerLeuProHis                                  260265270                                                                      HisAlaSerPheHisTyrAlaAsnCysGluGluGlnLysValGln                                  275280285                                                                      GlnGlnGlnGlnGlnGlnGlnGlnGlnGlnGlnGlnGlnLeuLeu                                  290295300                                                                      GlnGlnGlnLeuLeuGlnGlnGlnGlnGlnLysArgAsnLysAsp                                  305310315                                                                      GlyAspAspSerAlaSerProSerSerSerValThrAlaAsnGly                                  320325330                                                                      LysValLeuIleLeuAlaLysGluSerLeuGluMetValArgAsn                                  335340345                                                                      ValMetGlyValValAspSerThrLeuGlyLysAlaGluGluTrp                                  350355360                                                                      ValLysGlnLysGlnGluValLysGluMetIleArgGluArgPhe                                  365370375                                                                      LeuGlnGlnGlnGlnGlnTyrArgGlnGlnGlnGlnLysAspGly                                  380385390                                                                      AsnTyrValLysProSerGlnAspAsnValAspSerLysAsp                                     395400                                                                         __________________________________________________________________________ 

What is claimed is:
 1. A genetically engineered yeast cell of the genus Saccharomyces wherein all copies of the OPIl gene (SEQ ID NO: 1) are replaced, resulting in all copies of the OPIl gene (SEQ ID NO:1) being deleted.
 2. The yeast cell of claim 1 wherein the OPIl gene encodes the negative regulator Opilp.
 3. The yeast cell of claim 1 wherein the yeast cell is of the type Saccharomyces cerevisiae.
 4. The yeast cell of claim 2 wherein the OPIl gene has the nucleotide and amino acid sequence as shown in FIG. 8 (SEQ ID NOS 1-2).
 5. The yeast cell of claim 4 wherein the Opilp consists of 404 amino acid residues (SEQ ID NO: 2) and has a molecular weight of 40,036.
 6. The yeast cell of claim 5 wherein the Opilp contains polyglutamine tracts and a leucine zipper.
 7. A method for the enhanced production of inositol, inositol-containing metabolites or phospholipids in a genetically engineered yeast cell of the genus Saccharomyces, comprising the steps of:a. replacing all the copies of the OPIl gene (SEQ ID..NO:1) such that all copies of the OPIl gene (SEQ ID NO:1) are deleted in said yeast cell; b. culturing said yeast cell so as to allow for inositol, inositol-containing metabolites or phospholipids to be produced; and c. recovering said inositol, inositol-containing metabolites or phospholipids.
 8. The method of claim 7 wherein the yeast cell is a Saccharomyces cerevisiae cell.
 9. The method of claim 7 wherein the inositol, inositol-containing metabolites or phospholipids includes myo-inositol or inositol-1-phosphate.
 10. The method of claim 7 wherein the OPIl gene encodes the negative regulator Opilp.
 11. The method of claim 7 wherein the OPIl gene has the nucleotide and amino acid sequence as shown in FIG. 8 (SEQ ID NOS:1-2).
 12. The method of claim 10 wherein the Opilp consists of 404 amino acid-residues (SEQ ID NO:2) and has a molecular weight of 40,036.
 13. The method of claim 12 wherein the Opilp contains polyglutamine tracts and a leucine zipper. 